Installations for the continuous casting of steel slabs having these small thicknesses are distinguished from installations for the continuous casting of slabs of standard thickness (of the order of 150-200 mm), particularly by the presence, downstream of the ingot mold in the direction of withdrawal of the product, of at least one pair of rolls, called squeezing rolls. These have the function of bringing the product to its final thickness, without actual rolling, after it emerges from the ingot mold, by simply bringing the large faces of the cast product closer together. The ingot mold, whose design is derived from that of ingot molds for conventional continuous casting, does not, in fact, make it possible to directly produce the desired small thicknesses. The space between the squeezing rolls is fixed, in principle, throughout casting and is equal to the thickness desired for the product. They grip the product so as to bring about the advanced closing of the molten pool. On emerging from the rolls, the product is thus usually entirely solidified throughout its section. In any case, there is no longer any core in a completely molten state.
In order to achieve maximum thickness reduction, it is advantageous to locate the squeezing rolls directly at the exit from the ingot mold. However, this location is not without drawbacks. In particular, it risks giving rise to premature shrinking of the cast product from the cooled wall of the ingot mold in the final part of the latter, which may give result in a breakout. It is thus possible to design installations in which the squeezing rolls are sufficiently distant from the exit from the ingot mold, at a distance of the order of 1 m, for example.
One problem to be solved in the utilization of such a machine is the regulation of the depth of the molten pool (also called "metallurgical height"). As has been seen, the squeezing rolls are designed in order to shape a product whose core is still molten. If the molten pool is closed upstream of the squeezing rolls, these must thus act on a product which is entirely in the solid or mushy state. In order to bring the product to the desired thickness, they must undergo a severe separation force exerted by the product, which is, in fact, equivalent to an actual rolling on solid product. Such a force, if it is too great, or if it is repeated too frequently and over too long a period of time, can give rise to serious damage to the rolls themselves and their holding members. On the other hand, a machine capable of withstanding such great separation forces would scarcely be compatible in size with the rest of the casting installation due to the great rigidity of the frame which would be necessary. In any case, its cost would be far greater than that of a normal installation.